Process for Recovering Heavy Oil Utilizing One or More Membranes

ABSTRACT

An oil recovery process utilizes one or more membranes to remove silica and/or oil from produced water. In one method, the process includes separating oil from produced water and precipitating silica. The produced water having the precipitated silica is directed to a membrane, such as a ceramic membrane, which removes the precipitated silica from the produced water. In some cases, residual oil is present and is also removed by the membrane.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 12/488,118 filed Jun. 19, 2009, which is a continuation of U.S.patent application Ser. No. 12/199,283 filed Aug. 27, 2008, thedisclosures of which is hereby expressly incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a process for recovering heavy oil,more particularly, to an oil recovery process that utilizes a membraneprocess to remove silica and residual oil from produced water upstreamof water treatment and steam generation processes.

BACKGROUND

Conventional oil recovery involves drilling a well and pumping a mixtureof oil and water from the well. Oil is separated from the water, and thewater is usually injected into a sub-surface formation. Conventionalrecovery works well for low viscosity oil. However, conventional oilrecovery processes do not work well for higher viscosity, or heavy oil.

Enhanced Oil Recovery (EOR) processes employ thermal methods to improvethe recovery of heavy oils from sub-surface reservoirs. The injection ofsteam into heavy oil bearing formations is a widely practiced EORmethod. Typically, several tons of steam are required for each ton ofoil recovered. Steam heats the oil in the reservoir, which reduces theviscosity of the oil and allows the oil to flow to a collection well.Steam condenses and mixes with the oil, to form an oil-water mixture.The mixture of oil and water is pumped to the surface. Oil is separatedfrom the water by conventional processes employed in conventional oilrecovery operations to form produced water.

For economic and environmental reasons it is desirable to recycle theproduced water. This is accomplished by treating the produced water,producing a feedwater, and directing the treated feedwater to a steamgenerator or boiler and producing steam. The complete water cycleincludes the steps of:

-   -   injecting the steam into an oil bearing formation,    -   condensing the steam to heat the oil whereupon the condensed        steam mixes with the oil to form an oil-water mixture,    -   collecting the oil-water mixture in a well,    -   pumping the oil-water mixture to the surface,    -   separating the oil from the oil-water mixture to form produced        water,    -   treating the produced water to form feedwater for steam        generation equipment, and    -   converting the feedwater into steam having a quality of        approximately 70% to 100% for injecting into the oil bearing        formation.

Steam generation equipment can take various forms that generally includeeither once through steam generators (OTSG) or boilers of various types.However, treating the produced water to form a relatively pure feedwaterfor steam generation is challenging. In particular, treating theproduced water to retard or prevent silica scaling in purificationequipment, such as evaporators, and in steam generation equipment isdifficult.

Various approaches have addressed silica scaling. It is known thatchemically treating water to precipitate silica will reduce the silicaconcentration to a level that is suitable for use in producing steamusing Once Through Steam Generators (OTSG). This process is generallyreferred to as Warm Lime Softening followed by Ion Exchange. Silicaprecipitates as very fine crystals that are usually only several micronsin size. These fine silica crystals are difficult to economically removeby conventional mechanical separation devices such as deep bed filters,centrifuges, hydrocyclones, and gravity settlers. Another method is totrap the silica precipitates in a magnesium hydroxide and/or calciumcarbonate sludge that is created by addition of lime, magnesium oxide,and soda ash. This process has the disadvantage, however, of requiringlarge quantities of chemicals and producing large quantities of wastesludge. When used in this method, gravity settlers are sensitive tovariations in feed chemistry and are easily upset, creating problems fordownstream equipment.

It is also known to chemically treat the produced water and subjectchemically-treated produced water to an evaporation process thatproduces a distillate which becomes feedwater to an OTSG or boiler. Inparticular, it is known to use an evaporator and mechanical vaporcompressor to produce the distillate. In this particular approach, thepH of the produced water fed to the evaporator is raised to maintain thesolubility of silica. This prevents silica based scales from fouling theevaporator heat transfer surfaces. However, there are drawbacks anddisadvantages to this approach as well. The addition of caustic to raisethe pH represents a significant operating cost. Mechanical vaporcompression evaporators recover typically approximately 95% of the waterfrom the de-oiled produced water. The remaining 5% yields a concentratestream that is difficult to process. The pH is usually higher than 12,which makes the concentrate stream extremely hazardous. Any attempt toneutralize the stream causes the precipitation of silica solids whichare very difficult to separate from the aqueous solution. Theneutralization process is also known to release hazardous gases, such ashydrogen sulfide. These systems consequently tend to be expensive tooperate and costly to maintain.

SUMMARY OF THE INVENTION

The present invention relates to an oil recovery process that utilizesone or more membranes to remove silica and/or oil from produced water.In one embodiment, the process includes separating oil from the producedwater and precipitating silica onto crystals. The produced water havingthe precipitated silica is directed to a membrane, such as a ceramicmembrane, which removes the precipitated silica from the produced water.In some cases residual oil is present and may be removed by themembrane.

The present application also discloses a method of removing oil from anoil well and treating produced water including recovering an oil/watermixture from the well and separating oil from the oil/water mixture toproduce an oil product and the produced water. The method also includesmixing a crystallizing reagent with the produced water and precipitatingsolids from the produced water and forming crystals in the producedwater. A caustic is also mixed with the produced water to adjust the pHto approximately 9.5 to approximately 11.2. After mixing thecrystallizing reagent with the produced water, the produced water isdirected to one or more surrounding membranes. The method entailsfiltering the produced water with the ceramic membrane and producing aceramic membrane reject stream and a ceramic membrane permeate stream.After filtering the produced water with the ceramic membrane, directingthe ceramic membrane permeate stream to a reverse osmosis unit locateddownstream from the ceramic membrane. The method further includesfiltering the ceramic membrane permeate stream in the reverse osmosisunit to produce a reverse osmosis permeate stream and a reverse osmosisreject stream.

Also, the process or method of the present invention includes a processsimilar to that described above but wherein the ceramic membranepermeate stream is directed to an ion exchange unit located downstreamfrom the ceramic membrane. In this process, the ion exchange unit treatsthe ceramic membrane permeate stream so as to produce an ion exchangepermeate stream and an ion exchange reject stream.

The other objects and advantages of the present invention will becomeapparent and obvious from a study of the following description and theaccompanying drawings which are merely illustrative of such invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustrating basic process steps for recoveringheavy oil.

FIG. 2 is a schematic drawing showing a heavy oil recovery processutilizing a ceramic membrane to remove silica from produced water priorto an evaporation process.

FIG. 3 is a schematic representation of an oil recovery processutilizing reverse osmosis and evaporation with a ceramic membraneprocess to generate boiler feedwater.

FIG. 4 is a schematic representation of an oil recovery processutilizing ion exchange separation with a ceramic membrane process togenerate OTSG feedwater.

FIG. 5 is a schematic illustration of an oil recovery process utilizingat least two evaporators in series downstream from a ceramic membrane.

FIG. 6 is a schematic illustration similar to FIG. 5 but illustrating analternative process or method.

FIG. 7 is a schematic illustration of an oil recovery process utilizinga crystallization process and a ceramic membrane to filter concentratedbrine produced by an evaporator.

DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

The present invention entails a process for use in heavy oil recoveryfor cleaning produced water for steam generation. Heavy oil recovery isgenerally accomplished by injecting steam into heavy-oil bearingunderground formations. Steam heats the oil, thereby condensing. Theresulting oil-water mixture is pumped to the surface where the oil isseparated from the mixture leaving what is called produced water. Theproduced water is re-used to generate steam to feed back into theoil-bearing formation.

Produced water includes dissolved organic ions, dissolved organic acidsand other dissolved organic compounds, suspended inorganic and organicsolids, and dissolved gases. Typically, the total suspended solids inthe produced water is less than about 1000 ppm. In addition to suspendedsolids, produced water from heavy oil recovery processes includesdissolved organic and inorganic solids in varying portions. Dissolvedand suspended solids, in particular silica-based compounds, in theproduced water have the potential to foul purification and steamgeneration equipment by scaling. Additional treatment is thereforedesirable after oil-water separation to remove suspended silica-basedcompounds from the produced water. Hereinafter, the term “silica” willbe used to refer generally to silica-based compounds.

In order to prevent silica scaling and/or fouling of purification andsteam generation equipment, the present invention provides that producedwater be treated by using a ceramic membrane process to substantiallyremove silica from the produced water. The produced water, having silicaremoved, is further purified by any of a variety of purificationprocesses including reverse osmosis, evaporation, and ion exchangetreatment before being directed to steam generation equipment. Steamgeneration equipment may include at least boilers and once through steamgenerators.

Discussed herein are processes that utilize membranes, particularlyceramic membranes in oil recovery processes. A range of contaminants canbe removed from a waste stream with one or more membranes. In an oilrecovery process, for example, silica and residual oil in the producedwater are contaminants that may be effectively removed with membranes,particular ceramic membranes. In order to prevent silica scaling inpurification and steam generation equipment, the processes disclosedherein provide that produced water is treated by using a ceramicmembrane process to substantially remove silica from produced water orfrom other streams, such as a concentrate brine stream, that may beproduced in the process of treating a produced water stream. In the caseof produced water, after silica is removed, the produced water or otherresulting stream can be purified by any of a variety of purificationprocesses including reverse osmosis, evaporation, ion exchange oftreatment, after which the treated stream can be directed to steamgeneration equipment. Steam generation equipment may include boilers,once through steam generators, etc.

The general process of the present invention is illustratedschematically in FIG. 1, the schematic diagram denoted by the numeral100. Oil-water mixture 70 is directed to an oil-water separation processwhich effectively separates the oil from the water. This is commonlyreferred to as primary separation and can be carried out by variousconventional processes such as gravity or centrifugal separation.Separated water is subjected, in some cases, to a polishing de-oilingprocess where additional oil is removed from the water. Resulting waterfrom the oil-water separation process is referred to as produced water.Produced water contains residual suspended silica solids, emulsifiedoil, and dissolved solids. Produced water is directed via line 20 to aceramic membrane for silica removal. It should be pointed out thatsilica and residual oil can be removed simultaneously, or in stages withmultiple ceramic membranes. The ceramic membrane generates a permeatestream 30 and a reject stream 60A. The permeate from the ceramicmembrane is directed to a downstream purification process, such as anevaporation process. Reject stream 60A from the ceramic membrane isdirected to a waste line 60. The downstream purification processpurifies the permeate and produces a purified water stream 40 and areject or waste stream 60B. Purified water is directed to a steamgeneration process and the reject stream from the purification processis directed to a waste line 60. Steam is generated by the steamgeneration process and injected into the oil bearing formation to formthe oil-water mixture that is collected and pumped to the surface whereoil is separated therefrom.

FIGS. 2-4 illustrate various heavy oil recovery processes that utilizeceramic membranes to remove pollutants such as silica and oil from theproduced water. In the various processes illustrated, the produced wateris subjected to a crystallization process, prior to reaching the ceramicmembranes, for converting soluble silica to insoluble silica. Generally,the produced water is dosed with a crystal forming compound such asmagnesium oxide. The crystal forming compound forms crystals in theproduced water that adsorb silica, resulting in silica being driven orpulled out of solution and adsorbed on the formed crystals. Variouscrystal forming materials can be added. In some cases magnesium may beadded in the form of magnesium oxide or magnesium chloride. In anyevent, the magnesium compound forms magnesium hydroxide crystals thatfunction to sorb silica in the produced water, resulting in theconversion of silica from soluble to insoluble form. It should be notedthat in the case of magnesium that there is an insufficientconcentration of magnesium typically found in produced water to yield asubstantial amount of magnesium hydroxide crystals. Thus, in the case ofusing magnesium for crystal formation, the process generally requiresthe addition of magnesium to the produced water. Other reagents orcompounds may also be mixed with the produced water to remove silicathrough precipitation or adsorption. For example, ferric chloride,aluminum oxide, aluminum sulphate, calcium oxide or alum may be mixedwith the produced water. In some cases the dissolved silica and theproduced water can be removed from solution by mixing compounds with theproduced water where the compounds have surface active properties. Thesurface active properties may draw silica out of solution. Examples ofsuch compounds are oxides of aluminum, silica and titanium.

The pH of the produced water should be maintained in the range of 9.5 to11.2, and preferably between 10.0 and 10.8 for optimum precipitation ofsilica. Some caustic in the form of sodium hydroxide or sodium carbonatemay be added to trim the pH to a proper value. The duration of thecrystallization process only needs to be for a time period sufficient toprevent scaling of the downstream ceramic membrane or membranes.Duration does not have to be so long as to promote the growth of largesilica crystals.

Effectively, the crystallization process generates a suspension ofcrystals in the produced water. In the case of magnesium hydroxidecrystals, these crystals adsorb and pull silica out of solution,effectively precipitating the silica. The produced water with theprecipitated silica crystals, along with any insoluble silica that waspresent in the raw produced water, is directed to the ceramic membrane.The ceramic membrane produces a reject stream having the insolublesilica therein. Permeate produced by the ceramic membrane is directeddownstream for further purification or to a steam generation process. Aportion of the ceramic membrane's reject stream can be recirculated tothe ceramic membrane. Typically, about 1-10% of the water in the feedstream will pass through the ceramic membrane as permeate. A relativelyhigh recirculation rate will maintain a relatively high cross flowvelocity across the ceramic membrane, which will inhibit fouling.Recirculation of the reject stream is continued until the concentrationof the suspended solids in the reject stream reach approximately 1% to3% by weight. Once this level of solids concentration in the rejectstream is reached, then a selected flow of the reject stream can be bledoff and directed to a dewatering process for example. Water from thedewatering process can be directed back and mixed with the producedwater for continued treatment.

It is believed that the permeate from the ceramic membrane willtypically have a silica concentration in the range of 10-50 ppm and a pHof 9.5 to 11.2.

Turning now to a particular embodiment of the present invention, andreferring to FIG. 2, it is appreciated that the purification processincludes an evaporation process to which ceramic membrane permeate isdirected for further treatment. The evaporation process may beaccomplished utilizing any of a variety of evaporators, including, butnot limited to, falling film, forced circulation, multiple effects, andmechanical vapor recompression. The evaporation process generates adistillate stream 40 and a waste stream 60B. Depending on theevaporation process utilized, a concentrated brine recirculation loop(not shown) may be incorporated with the evaporator. Distillate waterstream 40 is directed to a boiler to produce steam stream 50 forinjection into the oil-bearing formation.

Prior to the produced water reaching the evaporation process, theproduced water is subjected to the crystallization process describedabove, and to treatment by a ceramic membrane or membranes generallyinterposed between the crystallization process and the evaporationprocess. Note in the FIG. 2 process where the ceramic membrane producesa reject stream 24 that is recycled for further treatment by the ceramicmembrane. Reject stream 24 is split into segments 24A and 24B. Note thatsegment 24A returns the reject to the ceramic membrane. That is, segment24A returns the reject to the ceramic membrane or to a point upstream ofthe ceramic membrane and downstream from the crystallization zone.Segment 24B returns reject to the crystallization zone. The return canbe directly to the crystallization zone or to a point upstream of thecrystallization zone and preferably downstream form the oil-waterseparation unit. Once the solids concentration in the reject stream 24has reached a selected level, portions of the reject stream are directedinto a waste stream 28 which leads to a dewatering process. Thedewatering process produces a concentrated waste stream 60 and a lessconcentrated stream 29 that is recycled to a point in the processupstream from the crystallization process. As described above, thecrystallization process, in combination with the ceramic membrane ormembranes, effectively removes soluble and insoluble silica, and in somecases residual oil, from the produced water prior to the produced waterreaching the evaporation process. This will generally inhibit fouling ofthe heat transfer surfaces of evaporators used in the evaporationprocess.

FIG. 3 illustrates another embodiment of the heavy oil recovery process.This process is similar to the process depicted in FIG. 2 with theexception that the evaporation process shown in FIG. 2 is replaced by areverse osmosis process that is interposed between the ceramic membraneand boiler, and an evaporation process that is interposed between thereverse osmosis process and the boiler. In the FIG. 3 process, thepermeate stream 30 from the ceramic membrane is directed to a reverseosmosis process. Here the reverse osmosis process produces a permeatestream 40 that is directed to the boiler, and also produces a rejectstream 34. The reject stream 34 from the reverse osmosis process isdirected into an evaporator which produces a distillate stream 36.Distillate from the distillate stream 36 is directed into the boiler.The evaporation process produces a blowdown or waste stream 60B that isdirected to the waste stream 60.

Again, the basic processes discussed above with respect tocrystallization and the ceramic membrane or membranes take place in theprocess of FIG. 3. Simply put, the crystallization process incombination with the ceramic membrane or membranes removes substantialsoluble and insoluble silica, and in some cases residual oil, in theproduced water prior to the produced water reaching the reverse osmosisprocess or the evaporation process.

Another embodiment, as illustrated in FIG. 4, includes ion exchangetreatment as a part of the purification process. Ceramic membranepermeate 40 is directed to an ion exchange process to produce an ionexchange effluent 32 and an ion exchange reject stream 34. Ion exchangeeffluent 32 is subjected to a de-aeration process to remove dissolvedgases. ion exchange reject stream 34 is directed back to produced waterstream 20. The de-aerated ion exchange effluent forms a purified waterstream 40 that is directed to a once through steam generator (OTSG) toproduce a steam-water mixture stream 42. Steam-water mixture stream 42is directed to a steam separation process where liquid is separated fromsteam, producing a liquid stream 44 and a steam stream 50. Liquid stream44 is directed back to the produced water stream 20 while the steamstream 50 is injected into the oil-bearing formation.

FIG. 5 illustrate an alternative process for purifying produced water ina heavy oil recovery process. In the case of the FIG. 5 process, thereis provided two evaporators 110, 112 generally interposed between thecrystallization step and boiler or steam generator. Each evaporator 110,112 includes a brine recirculation line 114, 116. Further theevaporators 110, 112 include distillate outlet lines 118, 120. It isappreciated that each evaporator 110, 112 produces steam which iscondensed to form distillate which in turn is directed from theevaporators 110, 112 via outlet lines 118 and 120. Distillate outletlines 118 and 120 are communicatively connected to a steam generatorfeed line 40 which in turn directs the distillate produced by theevaporators 110, 112 to the steam generator.

The process illustrated in FIG. 5 includes two ceramic membranes 130,132. Ceramic membrane 130 is interposed between the evaporators 110 and112 while membrane 132 is disposed downstream from evaporator 112. Abrine feed line 122 extends from brine circulation line 114 to ceramicmembrane 130. Brine feed line 124 extends from brine circulation line116 to ceramic membrane 132. A return line 140 directs a reject streamfrom one or both of the ceramic membrane 130,132 to a point upstream ofevaporator 110. As seen in FIG. 5, a portion of the concentrated brinebeing recirculated in lines 114 and 116 is directed to membranes 130 and132. Membranes 130 and 132 each produce a reject stream and a permeatestream. The permeate stream of ceramic membrane 130 is directed toevaporator 112 while the permeate stream of ceramic membrane 132 iswasted or directed to other points in the process for furtherpurification. Reject line 140 is split into segments 140A and 140B.Segment 140A returns the reject upstream to the evaporator 110. That is,segment 140A returns the reject to the evaporator 110 or to a pointupstream of the evaporator and downstream from the crystallization zone.Segment 140B returns reject to the crystallization zone. The return canbe directly to the crystallization zone or to a point upstream of thecrystallization zone and preferably downstream form the oil-waterseparation unit. Once the solids concentration in the reject stream 140has reached a selected level, portions of the reject stream are directedinto a waste stream 28 which leads to a dewatering process. Thedewatering process produces a concentrated waste stream 60 and a lessconcentrated stream 29 that is recycled to a point in the processupstream from the crystallization process. The reject stream fromceramic membrane 132 can be returned or recycled via line 142 to line140.

FIG. 6 illustrates a process that is similar to that discussed above andshown in FIG. 5. However, in the FIG. 6 embodiment, there is providedonly one ceramic membrane 130 and it is provided downstream from the twoevaporators 110, 112. In this case, the reject stream from the ceramicmembrane 130 is recycled via line 140 to the evaporator 110 or to apoint upstream of the evaporator 110. In addition, some of the rejectstream can be recycled to the crystallization zone or to a pointupstream of the crystallization zone via line 140B.

FIG. 7 is an alternative process 200 for removing silica, oil and otherdissolved and suspended solids in an oil recovery process. In thisexemplary process, an evaporator 202 receives an evaporator feed vialine 204. Line 204 directs produced water from the oil-water separatorsincluding conventional de-oiling, to the evaporator 202. Evaporator 202produces steam and a concentrated brine. The concentrated brine isrecirculated via line 206 through the evaporator. Evaporator 202produces steam which is condensed to form the distillate referred toabove and the distillate is directed through line 208 to a steamgenerator where steam is produced for injection into an oil bearingformation. To remove dissolved silica, residual oil and othercontaminants, at least a portion of the brine circulating in the brinerecirculation line 206 is treated. In this case there is provided brinetreatment line 210 that is communicatively connected to the brinerecirculation line 206. In the brine treatment line 210 there isprovided a crystallization reactor 212 and a ceramic membrane 214disposed downstream of the crystallization reactor. A certain amount ofthe brine circulating in line 206 is bled-off and directed into brinetreatment line 210. There the brine is subjected to a precipitation orcrystallization process in reactor 212. In one example, a crystallizingreagent such as magnesium oxide or magnesium chloride is added to thebrine and mixed with the brine by a mixer disposed in thecrystallization reactor. Also, the pH can be adjusted here by theaddition of a caustic such a sodium hydroxide. In any event, themagnesium oxide or magnesium chloride when mixed with the brine willform magnesium hydroxide. Magnesium hydroxide and silica co-precipitatein the crystallization reactor 212. The concentrated brine having theprecipitated silica is then directed to the downstream ceramic membrane214. There the ceramic membrane 214 produces a permeate stream that isdirected downstream from the ceramic membrane 214 through line 210 andreturned to the concentrated brine where it is mixed or joins theconcentrated brine for further recirculation through the evaporator 202.The ceramic membrane 214 also produces a reject stream that is directedinto reject line 216. The reject stream can be wasted, returned to theceramic membrane 214, or returned to the crystallization reactor 212. Insome cases it may be desirable to increase the concentration ofsuspended solids in the brine that reaches the crystallization reactor212. This can be accomplished by selectively controlling the amount ofreject pumped to line 216(B). In some cases it may be desirable tomaintain the concentration of suspended solids in the concentrated brinethat enters the crystallization reactor 212 at a concentration of 10,000mg/l and higher. In other cases it may be desirable to maintain thesuspended solid-concentration even higher, on the order of 20,000 to30,000 mg/l. Furthermore, since the reject stream leading from theceramic membrane 214 includes multiple segments 216(A), 216(B) and216(C), it follows that a portion of the reject can also be returned tothe ceramic membrane 214 or wasted through line 216(C). It also may bedesirable to waste a portion of the concentrated brine that forms a partof the permeate stream produced by the ceramic membrane 214. This isaccomplished by line 218 that leads from brine treatment line 210 to awaste line.

The present invention utilizes a ceramic membrane to substantiallyremove silica from produced water as part of a water cleaning andpurification process that produces steam for injection into oil-bearingformations. In the embodiments described, a ceramic membrane is utilizedupstream of other water purification processes. It is appreciated,however, that a ceramic membrane process may be utilized elsewhere insuch overall processes for removal of oil and other undesirablecontaminants from the water.

In the above description, reference is made to both a boiler and anOSTG. It is appreciated that various systems and processes can beutilized for generating steam for injection into the oil bearingformation. For example, reference is made to provisional patentapplication no. 60/890889 filed Feb. 21, 2007, the contents of which areexpressly incorporated herein by reference.

Details of the ceramic membrane are not dealt with herein because suchis not per se material to the present invention, and further, ceramicmembranes are known in the art. For a review of general ceramic membranetechnology, one is referred to the disclosures found in U.S. Pat. Nos.6,165,553 and 5,611,931, the contents of which are expresslyincorporated herein by reference. These ceramic membranes, useful in theprocesses disclosed herein, can be of various types. In some cases theceramic membrane may be of the type that produces both a permeate streamand a reject stream, On the other hand, the ceramic membranes may be ofthe dead head type, which only produces a permeate stream and fromtime-to-time the retentate is backflushed or otherwise removed from themembrane.

The structure and materials of the ceramic membranes as well as the flowcharacteristics of ceramic membranes varies. When ceramic membranes areused to purify produced water, the ceramic membranes are designed towithstand relatively high temperatures as it is not uncommon for theproduced water being filtered by the ceramic membranes to have atemperature of approximately 90° C. or higher.

Ceramic membranes normally have an asymmetrical structure composed of atleast two, mostly three, different porosity levels. Indeed, beforeapplying the active, microporous top layer, an intermediate layer with apore size between that of the support, and a microfiltration separationlayer. The macroporous support ensures the mechanical resistance of thefilter.

Ceramic membranes are often formed into an asymmetric, multi-channelelement. These elements are grouped together in housings, and thesemembrane modules can withstand high temperatures, extreme acidity oralkalinity and high operating pressures, making them suitable for manyapplications where polymeric and other inorganic membranes cannot beused. Several membrane pore sizes are available to suit specificfiltration needs covering the microfiltration, the ultrafiltration, andnanofiltration ranges from 1 micron down to 250 Dalton MWCO).

Ceramic membranes today run the gamut of materials (from alpha aluminato zircon). The most common membranes are made of Al, Si, Ti or Zroxides, with Ti and Zr oxides being more stable than Al or Si oxides. Insome less frequent cases, Sn or Hf are used as base elements. Each oxidehas a different surface charge in solution. Other membranes can becomposed of mixed oxides of two of the previous elements, or areestablished by some additional compounds present in minor concentration.Low fouling polymeric coatings for ceramic membranes are also available.

Ceramic membranes are typically operated in the cross flow filtrationmode. This mode has the benefit of maintaining a high filtration ratefor membrane filters compared with the direct flow filtration mode ofconventional filters. Cross flow filtration is a continuous process inwhich the feed stream flows parallel (tangential) to the membranefiltration surface and generates two outgoing streams.

A small fraction of feed called permeate or filtrate, separates out aspurified liquid passing through the membrane. The remaining fraction offeed, called retentate or concentrate contains particles rejected by themembrane.

The separation is driven by the pressure difference across the membrane,or the trans-membrane pressure. The parallel flow of the feed stream,combined with the boundary layer turbulence created by the cross flowvelocity, continually sweeps away particles and other material thatwould otherwise build up on the membrane surface.

The present invention may, of course, be carried out in other ways thanthose specifically set forth herein without departing from essentialcharacteristics of the invention. The present embodiments are to beconsidered in all respects as illustrative and not restrictive, and allchanges coming within the meaning and equivalency range of the appendedclaims are intended to be embraced therein.

1. A method of recovering oil from an oil well and treating producedwater comprising: recovering an oil/water mixture from the well;separating oil from the oil/water mixture to produce an oil product andthe produced water; mixing a crystallizing reagent with the producedwater and precipitating solids from the produced water and formingcrystals in the produced water; mixing a caustic with the produced waterto adjust the pH to approximately 9.5 to approximately 11.2; aftermixing the crystallizing reagent with the produced water, directing theproduced water to a ceramic membrane; filtering the produced water withthe ceramic membrane and producing a ceramic membrane reject stream anda ceramic membrane permeate stream; after filtering the produced waterin the ceramic membrane, directing the ceramic membrane permeate streamto a reverse osmosis unit located downstream from the ceramic membrane;and filtering the ceramic membrane permeate stream in the reverseosmosis unit to produce a reverse osmosis permeate stream and a reverseosmosis reject stream.
 2. The method of claim 1 wherein the ceramicmembrane and RO units are operatively connected, and wherein the ceramicmembrane permeate stream is directed directly from the ceramic membraneto the RO unit.
 3. The method of claim 1 wherein mixing acrystallization reagent with the produced water includes mixingmagnesium oxide, magnesium chloride or calcium oxide with the producedwater.
 4. The method of claim 1 wherein the produced water includessilica, and wherein mixing the crystallization reagent with the producedwater causes silica to precipitate from the produced water, and whereinthe formed crystals in the produced water adsorb silica.
 5. The methodof claim 1 including recycling at least a portion of the ceramicmembrane reject stream and mixing the crystallization reagent with atleast a portion of the ceramic membrane reject stream.
 6. The method ofclaim 5 including wasting at least a portion of the ceramic membranereject stream.
 7. A method of recovering oil from an oil well andtreating produced water comprising: recovering an oil/water mixture fromthe well; separating oil from the oil/water mixture to produce an oilproduct and the produced water; mixing a crystallizing agent with theproduced water and precipitating solids from the produced water andforming crystals in the produced water; mixing a caustic with theproduced water to adjust the pH to approximately 9.5 to approximately11.2; after mixing the crystallizing reagent with the produced water,directing the produced water to a ceramic membrane; filtering theproduced water with the ceramic membrane and producing a ceramicmembrane reject stream and a ceramic membrane permeate stream; afterfiltering the produced water in the ceramic membrane, directing theceramic membrane permeate stream to an ion exchange unit locateddownstream from the ceramic membrane; and treating the ceramic membranepermeate stream in the ion exchange unit to produce an ion exchangepermeate stream and an ion exchange reject stream.
 8. The method ofclaim 7 wherein the ceramic membrane and ion exchange unit areoperatively connected, and wherein the ceramic membrane permeate streamis directed directly from the ceramic membrane to the ion exchange unit.9. The method of claim 7 wherein mixing a crystallization reagent withthe produced water includes mixing magnesium oxide, magnesium chlorideor calcium oxide with the produced water.
 10. The method of claim 7wherein the produced water includes silica, and wherein mixing thecrystallization reagent with the produced water causes silica toprecipitate from the produced water, and wherein the formed crystals inthe produced water adsorb silica.
 11. The method of claim 7 includingrecycling at least a portion of the ion exchange reject stream andmixing the crystallizing reagent with at least a portion of the ionexchange reject stream.
 12. The method of claim 11 including wasting atleast a portion of the ion exchange reject stream.
 13. The method ofclaim 7 wherein mixing a crystallization reagent with the produced waterincludes mixing magnesium oxide, magnesium chloride or calcium oxidewith the produced water; and wherein the produced water includes silicaand wherein mixing the crystallization reagent with the produced watercauses silica to precipitate from the produced water, and wherein theformed crystals in the produced water absorb silica.
 14. The method ofclaim 1 wherein mixing a crystallization reagent with the produced waterincludes mixing magnesium oxide, magnesium chloride or calcium oxidewith the produced water; and wherein the produced water includes silicaand wherein mixing the crystallization reagent with the produced watercauses silica to precipitate from the produced water, and wherein theformed crystals in the produced water absorb silica.
 15. The method ofclaim 1 wherein the produced water includes silica and wherein mixingthe crystallizing reagent with the produced water forms a part at leastof a crystallization process; and wherein the crystallization process,in combination with the ceramic membrane, removes silica from theproduced water.
 16. The method of claim 15 wherein the crystallizationprocess, in combination with the ceramic membrane, removes soluable andinsoluable silica.
 17. The method of claim 15 wherein the produced waterincludes residual oil and wherein the crystallization process, incombination with the ceramic membrane, removes at least some residualoil from the produced water.